Hybrid circuit and electronic device using same

ABSTRACT

There is disclosed a hybrid circuit in which a circuit formed by TFTs is integrated with an RF filter. The TFTs are fabricated on a quartz substrate. A ceramic filter forming the RF filter is fabricated on another substrate. Terminals extend through the quartz substrate. The TFTs are connected with the ceramic filter via the terminals. Thus, an RF module is constructed.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a structure in which thin-filmtransistors (TFTs) are integrated with a ceramic device or with aferrite device. The invention disclosed herein can be used in asmall-sized, lightweight intelligent terminal typified by a mobile phonefor example.

[0003] 2. Description of the Prior Art

[0004] In recent years, research has been carried out on techniques forfabricating transistors, using a thin silicon film formed on a substrateof quartz or glass. Some of them have been commercialized. Thesetransistors are known as thin-film transistors (TFTs).

[0005] The main purpose of the research into TFTs is to use them inliquid crystal displays. Such a liquid crystal display has a number ofpixels arranged in rows and columns. TFTs are disposed as switchingdevices at the locations of the pixels. Electric charge held on pixelelectrodes is controlled by the TFTs.

[0006] A still advanced structure that is known has a peripheral drivercircuit consisting of TFTs, similarly to an active matrix circuit. Thisconfiguration achieves ever larger scales of integration.

[0007] Furthermore, it is considered to construct from TFTs circuits forhandling graphics information and for exchanging information with theoutside, as well as the peripheral driver circuit. Thus, the wholestructure is systematized.

[0008] Recently, intelligent terminals having variousinformation-processing functions have attracted attention. Theseintelligent terminals are also termed mobile computers and have variousfunctions such as communications functions (such as fax and telephone),information storage functions, and arithmetical processing functions.

[0009] The intelligent terminals described above are required to besmall and light enough to provide portability. In addition, they arerequired to have a thin-film display (also known as a flat paneldisplay) to handle graphics information. Of course, an intelligentterminal needs a circuit for exchanging information with an externaldevice.

[0010] It would be inevitable that more cordlessinformation-transmitting means are used. In particular, there is ademand for a function of exchanging information, using electromagneticwaves in the GHz band or higher permitting exchange of high-densityinformation. Accordingly, the intelligent terminal described above mustbe a small-sized, lightweight device incorporating a radio-frequencycircuit capable of sending and receiving electromagnetic waves in theGHz band.

[0011] Generally, this radio-frequency circuit comprises transistorsintegrated with a filter element (such as an inductor or capacitor inchip form or an SAW device). These transistors use a single-crystalsilicon wafer or compound semiconductors. In the future, more functionswill be required. Furthermore, smaller size, reduced weight, and lowercost will be necessitated. In spite of these technical trends, it is nowdifficult to increase the device density further.

SUMMARY OF THE INVENTION

[0012] It is an object of the present invention to provide a noveldevice in which a radio-frequency circuit capable of handling radiofrequencies in the GHz band is integrated with other component.

[0013] The present invention provides a device comprising a substratehaving TFTs fabricated on an insulating surface, terminals connectedwith the TFTs and extending through the substrate, and a laminateddevice connected with the terminals.

[0014] Also, the invention provides a device comprising a firstsubstrate having TFTs fabricated on an insulating surface and a secondsubstrate having a laminated device. These first and second substratesare bonded together. Terminals extend through the first substrate toconnect the TFTs with the laminated device.

[0015] The laminated device can consist of layers of magnetic ordielectric materials. One example of magnetic material is a ferrite thatis one kind of ceramic material.

[0016] In one preferred embodiment of the invention, the above-describedradio-frequency circuit is made up of TFTs, and the laminated deviceforms a filter circuit.

[0017] Heat generated by the TFTs can be effectively radiated by forminga heat-radiating layer on the first substrate. Preferably, theheat-radiating layer is made of a material of high thermal conductivitysuch as aluminum nitride.

[0018] Moreover, the invention provides a device comprising a firstsubstrate and a second substrate that are bonded together. The firstsubstrate has an insulating substrate on which TFTs are fabricated.Passive components are fabricated on the second substrate. Terminalsextend through the first substrate to connect the TFTs with the passivecomponents.

[0019] The heat-radiating layer can be made of aluminum nitride (AlN).Besides, the layer can be made of aluminum nitride to which oxygen isadded, (AlON). In addition, the layer can be made of crystallinecompounds of Si, Al, O, and N that are collectively known as SIALON.Further, the layer can be made of AlONC. These materials are effectivein relieving the stress between the substrate and the device andcontrolling the thermal conductivity, and have various featuresincluding electrical insulation, high thermal conductivity heatresistance and optical transparency.

[0020] In addition, the invention provides a device comprising first andsecond substrates bonded together. A circuit is fabricated from TFTs onthe bonded surface of the first substrate. Another circuit is fabricatedfrom a ceramic device on the bonded surface of the second substrate.These two circuits are connected together.

[0021] In this configuration, heat generated by the TFTs can beeffectively radiated by a heat-radiating layer formed on the firstsubstrate.

[0022] Also, the ceramic device can be fabricated, using a dielectric ormagnetic material. The ceramic device can be fabricated, using aferrite.

[0023] The heat-radiating layer can be made of aluminum nitride (AlN).Besides, the layer can be made of aluminum nitride to which oxygen isadded, or AlON. In addition, the layer can be made of crystallinecompounds of Si, Al, O, and N that are collectively known as SIALON.Further, the layer can be made of AlONC.

[0024] These materials are effective in relieving the stress between thesubstrate and the device and controlling the thermal conductivity, andhave various features including electrical insulation, high thermalconductivity, heat resistance, and optical transparency.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIGS. 1(A)-1(D), 2(A)-2(C) are cross-sectional views of TFTs,illustrating a process sequence for fabricating the TFTs in accordancewith the present invention;

[0026]FIG. 3(A) is a cross-sectional view of a hybrid circuit consistingof TFTs and an SAW filter, the hybrid circuit being built in accordancewith the invention;

[0027]FIG. 3(B) is an equivalent circuit diagram of the hybrid circuitshown in FIG. 3(A);

[0028]FIG. 3(C) is a plan view of the hybrid circuit shown in FIG. 3(A);

[0029] FIGS. 4(A)-4(D) are cross-sectional views of other TFTs,illustrating a process sequence for fabricating the TFTs in accordancewith the invention;

[0030]FIG. 5 is a cross-sectional view of a hybrid device consisting ofTFTs and an inductor, the hybrid device being built in accordance withthe invention;

[0031]FIG. 6 is a cross-sectional view of a hybrid device consisting ofTFTs and an SAW filter, the hybrid device being built in accordance withthe invention;

[0032]FIG. 7 is a view similar to FIG. 6, but showing another hybriddevice in accordance with the invention;

[0033]FIG. 8 is a graph illustrating the relation of the dimensions ofMOS transistors to their characteristics;

[0034]FIG. 9 is a fragmentary cross-sectional view of a marginal portionof a hybrid module in accordance with the invention;

[0035] FIGS. 10(A) and 10(B) are cross-sectional views of a hybriddevice consisting of TFTs and an SAW filter, the hybrid device beingbuilt in accordance with the invention;

[0036]FIG. 11(A) is an equivalent circuit diagram of the hybrid deviceshown in FIGS. 10(A) and 10(B);

[0037]FIG. 11(B) is an enlarged top view of the hybrid device shown inFIGS. 10(A) and 10(B);

[0038]FIG. 12 is a cross-sectional view of another hybrid deviceconsisting of TFTs and an SAW filter, the hybrid device being built inaccordance with the invention;

[0039]FIG. 13 is a fragmentary cross-sectional view of a marginalportion of a hybrid module in accordance with the invention;

[0040] FIGS. 14(A)-14(F) are views showing electronic devices eachincorporating a hybrid circuit including TFTs, the hybrid circuit beingbuilt in accordance with the invention; and

[0041]FIG. 15 is a block diagram of a mobile phone in accordance withthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Referring to FIG. 3(A), TFTs are integrated on a quartz substrate101. A ceramic device such as an SAW filter is fabricated in IC form onanother substrate 301. These two substrates are bonded together. Thequartz substrate 101 is provided with openings. The TFTs are connectedwith the ceramic devices via contact metal lines 206 extending throughthe openings. Thus, a module in which the TFTs are integrated with thepassive component, or the ceramic filter, can be constructed as shown inFIG. 3(B).

[0043] The passive component may also consist of inductor, capacitor,resistor, or other component. Furthermore, oscillating components may beintegrated.

[0044] Referring next to FIGS. 10(A) and 10(B), there is shown anotherhybrid device comprising a TFT circuit and an SAW filter component. TheTFT circuit is built on a quartz substrate 101. The SAW filter componentis fabricated on a quartz substrate 1034. These two substrates arebonded together, completing the hybrid device. In this way, the TFTcircuit is integrated with the ceramic device.

[0045] Integrating TFTs on a quartz substrate yields the followingadvantages:

[0046] (1) The substrate shape can be determined with high selectivity.

[0047] (2) Large areas can be accomplished.

[0048] (3) The components of an active matrix display can be integratedon the same substrate.

[0049] (4) The problems of stress occurring where the device density isenhanced can be mitigated.

Embodiment 1

[0050] A process sequence for the present embodiment is illustrated inFIGS. 1(A)-3(C). The present embodiment consists of TFTs integrated withan SAW (surface acoustic wave) filter. The SAW filter acts as a BPF(band-pass filter). In this embodiment, the TFTs form a CMOS circuithaving an output with which the SAW filter is connected.

[0051] First, an active layer, 103 and 106, for the TFTs is formed froma crystalline semiconductor, film such as silicon film, on a quartzsubstrate 101, as shown in FIG. 1(A), in a manner described below. Then,a gate insulator film 108 is formed by depositing a silicon oxide filmand a thermal oxide film in succession by plasma CVD.

[0052] Thereafter, aluminum metallization from which gate electrodeswill be formed is deposited. Then, a porous anodic oxide film, 109 and112, is formed by anodic oxidation. Subsequently, a dense anodic oxidefilm, 111 and 113, presenting a barrier is formed by anodic oxidation.Also, gate electrodes 110 and 114 are created.

[0053] The qualities of these two kinds of anodic oxide can bedetermined by selection of the kind of the electrolyte used during theanodization. In this way, a state as shown in FIG. 1(A) is obtained.

[0054] Then, dopant elements are implanted under such conditions thatsource and drain regions are formed. In this embodiment, a P-channel TFTis formed to the left, while an N-channel TFT is formed to the right.This processing step is carried out by selectively implanting the dopantelements for imparting P- and N-type conductivities by a plasma dopingmethod, while selectively masking regions where TFTs are to befabricated with a resist mask.

[0055] In this processing step a source region 102 and a drain region104 for the P-channel TFT are formed by self-alignment techniques.Similarly a source region 107 and a drain region 105 for the N-channelTFT are formed in a self-aligned manner.

[0056] Then, the porous anodic oxide film, 109 and 112, is selectivelyremoved. Thus, a state as shown in FIG. 1(B) is obtained. Under thiscondition doping is again done but with a lower dose. During thisfabrication step, regions 115, 119, 122, and 126 are lightly doped. Theregions 115 and 119 become lightly doped regions for the P-channel TFT.The regions 122 and 126 become lightly doped regions for the N-channelTFT. Also formed are offset gate regions 116, 118, 123, 125 and channelregions 117, 124. As a result, the state of FIG. 1(B) is derived.

[0057] Then, a silicon nitride film 128 is formed as an interlayerdielectric film by plasma CVD. Subsequently, a polyimide resinous film129 is spin-coated.

[0058] Where the interlayer dielectric film is made from a resinousmaterial, the surface can be planarized. This is favorable for laterformation of conductive interconnects. The resinous material can beselected from polyamide, polyimidamide, acrylic resin, epoxy resin, aswell as polyimide.

[0059] In consequence, a state as shown in FIG. 1(C) is obtained.Contact holes are formed. Also, source electrode and sourceinterconnects 130 for the P-channel TFT, source electrode and sourceinterconnects 132 for the N-channel TFT, and drain electrode and draininterconnects 131 common to both TFTs are formed.

[0060] In this manner, a state shown in FIG. 1(D) is derived. The rearsurface of the quartz substrate 101 is polished to thin the substrate asshown in FIG. 2(A).

[0061] Then, openings 201 extending to the drain electrode and draininterconnects 203 are formed, as shown in FIG. 2(B). Electrode terminals206 extending to the rear surface of the substrate 101 through theopenings 201 are formed as shown in FIG. 2(C). This is followed byformation of an aluminum nitride film 205 acting to radiate heatgenerated from the TFTs.

[0062] After obtaining the state shown in FIG. 2(C), the quartzsubstrate 101 and the quartz substrate 301 having the SAW filter thereonare bonded together via an adhesive layer 306, as shown in FIG. 3(A).This adhesive layer 306 may comprise an adhesive binder in which fineparticles having electrical conductivity are dispersed. The adhesivelayer exhibits electrical conductivity in the direction of thickness.

[0063] The SAW filter is fabricated by forming a barium titanate film302 on the quartz substrate 301. Comb-shaped electrodes 303 and 304having a pattern as shown in the top view of FIG. 3(C) are created. Aninterlayer dielectric film 307 is made from a resinous material.

[0064] One electrode 303 of the SAW filter has a contact electrode 305coming into contact with an electrode terminal 206 extending through thequartz substrate 101 having the TFTs thereon.

[0065] The configuration of FIG. 3(A) is represented in terms of anequivalent circuit of FIG. 3(B). This circuit comprises a CMOS circuitand a band-pass filter connected to the output of the CMOS circuit. Thefilter consists of the SAW filter.

[0066] The structure of the present embodiment permits various circuitsmade up of transistors to be integrated with a filter component, thusbuilding a modular construction. Consequently, a radio-frequency modulethat can be used in a mobile phone or in a portable intelligent terminalcan be accomplished.

[0067] Use of such modularized components makes it possible to reducethe sizes of mobile phones and portable intelligent terminals. Inaddition cost reductions can be achieved.

[0068] PROCESS SEQUENCE FOR TFTS

[0069] A process sequence for fabricating the TFTs up to the state shownin FIG. 1(A) is described now. First, as shown in FIG. 4(A), anamorphous semiconductor film, such as a silicon film 402 is formed to athickness of 500 Å on the quartz glass substrate 101 by LPCVD. It isimportant that the surface of the quartz substrate have a sufficientdegree of flatness.

[0070] Then, a mask 403 is fabricated from a silicon oxide film.Openings 404 are formed in this mask 403. The amorphous silicon film 402is exposed at these openings 404 that are elongated in the rearwarddirection as viewed in the figure.

[0071] Then, nickel acetate salt solution containing 100 ppm (by weight)nickel is applied by spin-coating. As a result, nickel is maintained incontact with the surface (FIG. 4(A)). The nickel can be introduced byCVD, sputtering, plasma processing, ion implantation, or other method.Besides the nickel, other element selected from the group consisting ofFe, Co, Ru, Rh, Pd, Os, Ir, Pt, Cu, and Au can be used.

[0072] Thereafter, a heat treatment is conducted at 600° C. for 8 hoursin a nitrogen ambient at normal pressure. During this processing step,crystal growth progresses in a direction indicated by 405 parallel tothe substrate (FIG. 4(B)).

[0073] This heat treatment is carried out in an electric furnace,resulting in a multiplicity of pillar-shaped crystalline structureshaving diameters of tens to hundreds of nanometers. These crystallinestructures are arrayed parallel to each other. The longitudinaldirection of these crystalline structures agrees with the crystal growthdirection indicated by 405. These crystalline structures are partitionedfrom each other by crystal grain boundaries extending along thesecrystalline structures. We have confirmed that these crystal grainboundaries are inactive. The above-described heat treatment can beperformed at a temperature between approximately 450 and 1100° C.

[0074] On completion of the heat treatment for the crystallization themask of silicon oxide film 403 is removed. Then, a heat treatment isconducted at 950° C. for 20 minutes in an oxygen ambient containing 3%by volume of HCl. During this processing step, a thermal oxide filmgrows to a thickness of 200 Å. The thickness of the silicon filmdecreases from 500 to 400 Å. Importantly, the thermal oxidation isperformed at a heating temperature of 800 to 1,100° C., preferably 900to 1,100° C.

[0075] In this process, as the thermal oxide grows, the number ofdangling bonds of silicon atoms decreases, thus greatly reducing thedefects in the film. This process step for forming the thermal oxide isimportant and assures that the final TFTs have excellentcharacteristics. This thermal oxide film contains a richer amount ofnickel than the silicon film. Observation with an electron microscopehas revealed that the formation of this thermal oxide film producesapparently cylindrical crystalline structures.

[0076] After the completion of the formation of the thermal oxide film,it is removed. In this way, the nickel element can be eliminated.

[0077] The obtained crystalline silicon film is patterned into shapes103 and 106 shown in FIG. 4(C). The shape 103 forms an active layer forP-channel TFT and the shape 106 forms an active layer for N-channelTFTs. Then a silicon oxide film (CVD oxide film) is grown to 200 Å byplasma CVD to form a gate insulator film 409. Then, second thermaloxidation is conducted to form a thermal oxide film.

[0078] During this step for forming the thermal oxide film, a heattreatment is conducted at 950° C. for 20 minutes in an oxygen ambientcontaining 3% by volume of HCl. During this processing step, a thermaloxide film is grown to a thickness of 200 Å.

[0079] This thermal oxide film is formed inside the previously grown CVDoxide film i.e., close to the boundary with the active layer. Thus, thethermal oxide film and the CVD oxide film are laminated from the inside,resulting in the gate insulator film 409. The thickness of the finalactive layer is 300 Å (FIG. 4(C)).

[0080] Then, an aluminum film containing a trace amount of scandium isformed to a thickness of 400 nm (4000 Å) by sputtering and patternedinto shapes 410 and 411 (FIG. 4(D)) from which gate electrodes will beformed. The TFTs show characteristics comparable or superior to those ofMOS transistors using a single-crystal silicon wafer.

[0081] Indicated by the solid line in FIG. 8 is one example ofcharacteristic of a TFT having a gate insulator film having a thicknessof 30 nm (300 Å) and a channel length of 0.6 μm. This TFT was fabricatedwith 2-μm design rules. To shorten the channel length, the side surfacesof the gate electrodes are anodized.

[0082] Plotted on the horizontal axis is the voltage applied from apower supply. Plotted on the vertical axis is delay time correspondingto the inverse of the operating speed. As the delay time decreases,higher-speed operation is possible.

[0083] Indicated by the broken lines in FIG. 8 are data about MOStransistors using a single-crystal silicon wafer, comparing thesetransistors. The comparison data shown in FIG. 8 illustrate the scalingprinciples i.e., the relation between the dimensions (or, the channellength and the thickness of gate insulator film) and the delay time. Thescaling principles are based on the concept that as the dimensions ofMOS transistors are reduced, their radio-frequency characteristics areenhanced according to a certain rule. Of course, the principles are notstrict ones.

[0084] The plotted points indicated by the broken lines in FIG. 8roughly obey the scaling principles. It can be seen that the RFcharacteristics of the TFT fabricated by a method in accordance with thepresent invention are higher than those forecasted from the prior artscaling principles by plural orders of magnitude. If the scalingprinciples for the MOS transistor using a single-crystal silicon waferare obeyed, the delay time of the TFT plotted by the solid lines shouldis have greater values.

[0085] For example, if the conventional scaling principles are observed,the delay time of a MOS transistor having a channel length of 0.6 μm anda gate insulator film thickness (tox) of 30 nm should be greater than atleast the plotted delay time of a device having a channel length of 0.5μm and a gate insulator film thickness (tox) of 11 nm. In this way, theTFT disclosed herein has characteristics exceeding those of the priorart MOS transistor.

Embodiment 2

[0086] The present embodiment gives an example in which theconfiguration of FIG. 3(A) uses one or more substrates made of aceramic. All the substrates can be made of a ceramic. Alternatively, thesubstrate on which TFTs or an SAW device is fabricated may be made of aceramic. Where a ceramic substrate is employed, there is a wider choiceof materials. This is advantageous for productivity and cost.

[0087] Where a ceramic substrate is used, it is important to select asubstrate having excellent surface flatness. Especially, the substrateon which TFTs are fabricated must be free from pinholes in addition tohaving excellent surface flatness.

Embodiment 3

[0088] The present embodiment gives an example in which the band-passfilter (BPF) consisting of an SAW filter is replaced by an inductor.FIG. 5 schematically shows the construction of the present embodiment.Those parts that are the same as shown in FIG. 3 have the samestructures as shown in FIG. 3.

[0089] In FIG. 5, conductor patterns 502 form an inductor. A dielectric501 exists between the successive conductor patterns. A pattern 504forms one terminal of the inductor and is connected with the output ofthe invertor consisting of P- and N-channel TFTs. A pattern 503 formsanother terminal of the inductor and extends to other components andconductive interconnects (not shown). A substrate 500 is made of aceramic material.

[0090] In this embodiment, an inductor is disposed. Other devices suchas chip capacitor, device using a piezoelectric material (e.g.,voltage-controlled oscillator (VCO)), and devices exploiting ferrite canbe disposed.

Embodiment 4

[0091] The present embodiment is a modification of the configuration ofFIG. 3. The construction of the present embodiment is schematicallyshown in FIG. 6. The present embodiment is characterized in that analuminum film 602 is formed on an aluminum nitride film 601. Thus, heatgenerated by TFTs can be radiated at improved efficiency. This is usefulin operating the TFTs at high speeds.

Embodiments 5

[0092] The present embodiment Dives an improvement of the configurationof Embodiment 4. The configuration of the present embodiment isschematically shown in FIG. 7. The present embodiment is characterizedin that an aluminum nitride film 702 is formed on a quartz substrate701. Consequently, heat generated by the active layers of TFTs can beeffectively radiated.

Embodiments 6

[0093] The present embodiment pertains to a structure of a modularmarginal portion of the construction shown in FIG. 3(A). That is, thepresent embodiment relates to a method of mounting the module shown inFIG. 3(A) where the module is used for an apparatus.

[0094]FIG. 9 shows the structure of the modular marginal portion shownin FIG. 3(A). In FIG. 9, a conductive interconnect 130 extending fromthe source or drain of a TFT is connected with an extraction electrode(extraction terminal) 901, which in turn is used for connection with anexternal device.

[0095] Ceramic devices and other devices are fabricated on a substrate301. Conductive interconnects 903 are also formed on the substrate 301and connected with an extraction electrode (extraction terminal) 902,which in turn is connected with an external device. The conductiveinterconnects 903 are connected with an SAW device or inductor built onthe substrate 301. Because of the structure described thus far, themodularized substrate can be directly inserted into a connector terminalof an apparatus. Furthermore, the apparatus can find wider application.In addition, the production cost can be reduced.

Embodiment 7

[0096] The present embodiment is similar to the configuration of FIG. 7except that a quartz substrate 701 is polished completely and that analuminum nitride film 702 is used as a TFT substrate. The aluminumnitride film 702 is required to be rigid enough to be used as asubstrate alone at least until the stage where this substrate is bondedto the substrate 301. In this structure, heat generated by the TFTs canbe radiated more effectively.

Embodiments 8

[0097] The present embodiment provides the structure shown in FIG. 3(A)and is further characterized in that an active matrix liquid crystaldisplay in an integrated form is fabricated on other portion (notshown). An active matrix circuit (not shown) is formed on the otherportion of the quartz substrate 101 of FIG. 3(A). This quartz substrate101 is used as a TFT substrate. Another substrate (not shown) that istransparent is employed as a counter substrate. These two substrates arecemented together via a liquid crystal material layer, thus completingthe active matrix liquid crystal display. In this structure, the displaydevice is modularized, in addition to the RF circuit.

Embodiments 9

[0098] A process sequence for the present embodiment is illustrated inFIGS. 10(A)-11(B). In this embodiment, a TFT circuit is integrated withan SAW (surface acoustic wave) filter acting as a band-pass filter(BPF). In this specific embodiment, the SAW filter is connected with theoutput of a CMOS circuit.

[0099] First, a state as shown in FIG. 1(D) is obtained in the same wayas in Embodiment 1. Then, an aluminum nitride film 1033 is formed overelectrodes and conductive interconnects 130-132, as shown in FIG. 10(A).This aluminum nitride layer serves as a heat-radiating layer and also asa protective layer.

[0100] Then the counter substrate having the SAW filter thereon isformed and bonded to the substrate 101. The counter substrate, 1034, ismade of a ceramic or other appropriate material. A dielectric material1035 consisting of barium titanate and electrodes 1036 are formed on thecounter substrate 1034. Indicated by 1037 are contact electrodes.

[0101]FIG. 11(B) is a top view of the SAW filter, which comprisescomb-shaped electrodes 1036 and 1101 interdigitating each other on thedielectric material. This substrate 1034 is bonded to the substrate 101via an adhesive layer 1038, thus completing a hybrid circuit of the TFTcircuit and the SAW filter (FIG. 10(B)). FIG. 11(A) is an equivalentcircuit diagram of the construction of FIG. 10(B).

[0102] Use of the configuration of the present embodiment makes itpossible to integrate and modularize various circuits made up of TFTsand a filter component. In this way, an RF module used in a mobile phoneor portable intelligent terminal can be accomplished. Such modularizedcommercial products permit miniaturization of mobile phones and portableintelligent terminals. Furthermore, lower costs can be achieved.

[0103] While the above embodiment gives an example in which an SAWfilter is integrated with other circuits, other filters such asinductors, chip capacitors, and filters using ferrite can be integratedwith other circuits.

Embodiment 10

[0104] The present embodiment is based on the structure of FIG. 10(B)and further characterized in that heat generated by the TFTs can beradiated more effectively. As shown in FIG. 12, an aluminum nitride film1201 is formed on the substrate having the TFTs thereon. In thisstructure, the active layers of the TFTs are in direct contact with thecooling layer. This can further enhance the heat-radiating effect.

Embodiment 11

[0105] The present embodiment gives a structure utilized where theconfiguration of FIG. 11(A) is used as a module. FIG. 13 shows amarginal portion of the module. A conductive interconnect 1310 extendingfrom the source or drain of a TFT is shown to be connected with anextraction electrode (extraction terminal) 1313, which in turn isconnected with an external device. Similarly, a conductive interconnect1311 extending from a ceramic device or the like is shown to beconnected with an extraction electrode (extraction terminal) 1312, whichin turn is connected with an external device. Because of the structuredescribed thus far, the modularized substrate can be directly insertedinto a connector terminal of an apparatus. Furthermore, the apparatuscan find wider application. In addition, the production cost can bedecreased.

Embodiment 12

[0106] The present embodiment is based on the structure shown in FIG.10(B) and characterized in that an active matrix liquid crystal displayin an integrated form is formed on other portion (not shown). A liquidcrystal material layer is sandwiched between the two substrates and thusthe liquid crystal display can be disposed at this location. An RFcircuit made up of TFTs and passive components can be integrated withthe active matrix liquid crystal display. This structure is preferableas a component of a portable intelligent terminal.

Embodiment 13

[0107] The present embodiment gives an example of electronic devicemaking use of a hybrid circuit of TFTs, passive components, and aceramic device. FIG. 14(A) shows a portable intelligent terminal havinga communications function utilizing a telephone network. The body 2001of this electronic device incorporates an integrated circuit 2006consisting of a hybrid circuit disclosed herein. The body furtherincludes an active matrix liquid crystal display 2005, a camera portion2002 for accepting images, an image pickup portion 2003, and controlswitches 2004.

[0108] Referring to FIG. 14(B), there is shown a head mounted displaythat is one kind of electronic device. The user wears this displaydevice on his or her head. An image is displayed in front of the eyes byvirtual reality technology. The body, 2101, of the display device isattached to the head by a band 2103. The image is created by liquidcrystal displays 2102 corresponding to the left and right eyes,respectively. Since this electronic device must be small andlightweight, the hybrid circuit disclosed herein is adapted to be usedin this electronic device.

[0109] Referring next to FIG. 14(C), there is shown a display devicehaving a function of displaying map information and other kinds ofinformation according to signals sent from artificial satellites.Information sent from an artificial satellite is received by an antenna2204 and processed by an electronic circuit incorporated in the body2201. Requisite information is displayed on a liquid crystal displayportion 2202. The display device is controlled, using control switches2203. This display device is required to be devised so that the wholestructure is miniaturized. Therefore, it is useful to use the hybridcircuit disclosed herein.

[0110] Referring next to FIG. 14(D), there is shown a mobile phone whosebody is indicated by 2301. The body 2301 of this electronic device hasan antenna 2306, a speech output portion 2302, a liquid crystal display2304, control switches 2305, and a speech input portion 2303. It isuseful for this electronic device to use the hybrid circuit disclosedherein in reducing the size of the whole construction.

[0111]FIG. 15 is a block diagram of the electronic device shown in FIG.14(D). The body of this device is indicated by numeral 301. In receptionmode, electromagnetic waves are received by an antenna 3002 and sent toan RF input/output portion 3003. Then, the signals are supplied to aspeech-processing portion 3006 via all of an RF control portion 3007, amodulating/demodulating portion 3004, and a channel coding portion 3005.The modulating/demodulating portion 3004 is under control of a CPU 3008.The speech-processing portion 3006 drives a loudspeaker 3010, which inturn produces audible information.

[0112] In oscillation mode, speech information is entered from amicrophone 3009 and produced as electromagnetic waves from the antenna3002 after passing through the route opposite in direction to theforegoing.

[0113] Referring next to FIG. 14(E), there is shown a video camera thatis one kind of portable image pickup device. The body of this electronicdevice is indicated by reference numeral 2401 and has an openablemember. A liquid crystal display 2402 and control switches 2404 areattached to the openable member. The body 2401 further includes an imagepickup portion 2406, an integrated circuit 2407, a speech input portion2403, operation switches 2404, and batteries 2405. It is useful for thiselectronic device to use the hybrid circuit disclosed herein in reducingthe size of the whole construction. Especially, where an additionalfunction such as a communications function is incorporated, it isnecessary to incorporate an RF circuit in IC form for the addedfunction. For this reason, the invention disclosed herein can beexploited beneficially.

[0114] Referring next to FIG. 14(F), there is shown a projection typeliquid crystal display that is another kind of electronic display. Thebody of this electronic display is indicated by numeral 2501 and has alight source 2502, a liquid crystal display 2503, and optics 2504. Thisprojection type liquid crystal display has a function of projecting animage onto a screen 2505. Projection type displays are also required tobe reduced in size and weight. Therefore, it is useful to exploit thepresent invention disclosed herein.

[0115] The above-described liquid crystal displays for electronic devicecan be either of the transmissive type or of the reflective type. Thetransmissive type is advantageous to achieve higher displaycharacteristics. On the other hand, the reflective type is advantageouswhere lower power consumption, smaller size, and reduced weight aresought for. Additionally, an active matrix electroluminescent displayand a flat panel display such as a plasma display can be used as displaydevices.

Embodiment 14

[0116] The present embodiment is based on the configuration ofEmbodiment 1 or 9 and characterized in that polycrystalline siliconwafers are used as substrates. All the substrates can be made of apolycrystalline silicon wafers. Alternatively, only the substrate onwhich TFTs or an SAW device is fabricated may be made of apolycrystalline silicon wafer. Polycrystalline silicon wafers areavailable at much lower costs than quartz substrates. Accordingly, thiscan contribute greatly to decreases in the costs of circuits andapparatus.

[0117] In the present embodiment, a silicon oxide film is grown to athickness of 1 μm on a polycrystalline silicon wafer by plasma CVD.Then, thermal oxidation is carried out to form a thermal oxide film to athickness of 50 nm (500 Å). Thus, a silicon oxide film having a flatsurface and excellent interface characteristics can be grown on thepolycrystalline silicon wafer. Using this silicon oxide film as a baselayer TFTs are fabricated on it.

[0118] Forming the thermal oxide film directly on the polycrystallinesilicon film and using this thermal oxide film as a base layer isundesirable, because the surface of the thermal oxide is made uneven dueto the polycrystalline structure of the substrate. This would adverselyaffect the fabrication of the TFTs and hence their characteristics. Itis possible to use a single-crystal silicon wafer instead of apolycrystalline silicon wafer. In this case, however, the advantage oflow cost is sacrificed.

[0119] The present invention provides a novel structure in which an RFcircuit capable of handling high frequencies in the GHz band can befabricated in IC form. In particular, connector terminals or conductiveinterconnects extend through a substrate having TFTs thereon. Alaminated device formed on another substrate is connected with theseconnector terminals. In consequence, a small-sized, RF module can beobtained in IC form. Utilizing the module in accordance with theinvention, portable intelligent terminals can be made smaller in sizeand weight. Furthermore, lower costs can be accomplished.

What is claimed is:
 1. A hybrid circuit comprising: a substrate havingan insulating surface on which at least one TFT is fabricated; terminalsextending through said substrate and connected with said TFT; and alaminated device connected with said terminals.